Tomographic image capturing device

ABSTRACT

The tomographic image capturing device of the present invention is configured to: split light from a light source ( 11 ) into measurement light and reference light; cause the measurement light and the reference light to be incident to an object (E) and a reference object ( 49 ), respectively; and capture tomographic images of the object (E) on the basis of interference light generated by superposition of the measurement light reflected from the object (E) and the reference light reflected from the reference object ( 49 ). The tomographic image capturing device has a first image capturing mode and a second image capturing mode. The first and second image capturing modes are each a mode in which the measurement light is two-dimensionally scanned to be incident to the object (E) and the tomographic images of the object (E) are captured. The two-dimensional scans in the second image capturing mode require a shorter time than that required for the two-dimensional scans in the first image capturing mode. The capturing of the tomographic images in the first image capturing mode is performed after performing adjustment of an image capturing condition necessary for capturing the tomographic images in the first image capturing mode. The adjustment is based on the tomographic images captured in the second image capturing mode.

TECHNICAL FIELD

The present invention relates to a tomographic image capturing device that captures a tomographic image of an object such as a subject's eye on the basis of interference light generated by superposition of measurement light from the object and reference light.

BACKGROUND ART

As a type of ophthalmic diagnostic equipment, there are tomographic image capturing devices that utilize optical interference of so-called OCT (Optical Coherence Tomography) to capture tomographic images of ocular fundi. Such tomographic image capturing devices can capture tomographic images of ocular fundi at high sensitivity through irradiating the ocular fundi with broadband and low coherent light and causing the reflected light from the ocular fundi to interfere with reference light. When the horizontal direction, vertical direction and depth of an ocular fundus are represented by x-direction, y-direction and z-direction, respectively, such a tomographic image capturing device can acquire tomographic pictures (B-scan pictures) in the xz-directions. In ordinary image capturing of OCT, the tomographic images are captured, for example, at a rate of 40 images per second and a set of 100 or more tomographic pictures of a retina can be acquired by one-time testing (image capturing at a part of the retina).

In general, when capturing tomographic images, adjustment of an image capturing condition, such as positioning of an image capturing site and reference mirror, focus adjustment, and determination of a dispersion compensation glass, may be performed before the image capturing so that optimum tomographic pictures of an ocular fundus are obtained. As illustrated in FIG. 7, when raster scans are performed for image capturing of a three-dimensional tomographic structure, there is a method in which adjustment of the image capturing condition before the image capturing is performed while observing tomographic pictures obtained by sequentially scanning only in a fast axis direction (x-direction) at the center of a scanning field angle that is two-dimensionally set, and thereafter the original scanning field angle area as a whole is raster-scanned at the time of actually capturing tomographic images. In such a method, the tomographic pictures obtained at the time of adjustment of the image capturing condition are approximately fixed and the form variation of the image capturing site is less likely to occur in the tomographic pictures. Therefore, adjustment can easily be performed for the appearance position of the image capturing site in the tomographic pictures and for the image capturing condition, such as focus adjustment, which may be advantageous.

On the other hand, when the raster scan area is wide, when the object is an eye of high myopia, when images of the peripheral area of a retina are captured, when images of an area of optic papilla are captured, or in similar cases, the curvature of captured tomographic pictures is large, so that the appearance positions of the image capturing site in the tomographic pictures significantly differ in accordance with the scanning position. Therefore, an appropriate focus position and reference mirror position cannot be determined even if the image capturing condition is optimized by performing adjustment of the image capturing condition on the basis of the tomographic pictures obtained only by scanning the center position of the raster scans because the form of the measurement object cannot be perceived except the center position of the raster scans. As a result, in the tomographic pictures obtained by scanning other parts than the center position of the raster scans, defocus and/or replication of the tomographic structure of the image capturing site may possibly occur. In addition, if the appearance position of image capturing site is unnecessarily set below to prevent such replication, the image contrast may deteriorate.

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

If, also at the time of adjusting the image capturing condition, the raster scan area as a whole is scanned as in the capturing of tomographic images, all of the tomographic pictures of the image capturing site can be observed during the adjustment of the image capturing condition and an optimum image capturing condition can thus be determined. This is said to be ideal. However, the raster scans of the scanning area as a whole take time and the adjustment of image capturing condition accordingly requires a long period of time. The actual capturing of tomographic images is after performing adjustment of the image capturing condition to optimize the image capturing condition, and the sequence of image capturing operations takes time, which may restrain the subject from moving until the image capturing is completed. Therefore, the image capturing operations may readily be affected by the disturbance such as involuntary eye movements. If large involuntary eye movements occur, adjustment of the image capturing condition will be necessary again. This may lead to a negative spiral that the image capturing requires a longer period of time.

The present invention has been made in consideration of the above and an object of the present invention is to provide a tomographic image capturing device that can complete adjustment of the image capturing condition in a short time to determine an optimum image capturing condition.

Means for Solving the Problems

To achieve the above object, a first aspect of the present invention provides a tomographic image capturing device configured to: split light from a light source into measurement light and reference light; cause the measurement light and the reference light to be incident to an object and a reference object, respectively; and capture tomographic images of the object on the basis of interference light generated by superposition of the measurement light reflected from the object and the reference light reflected from the reference object, the tomographic image capturing device having a first image capturing mode and a second image capturing mode, the first and second image capturing modes each being a mode in which the measurement light is two-dimensionally scanned to be incident to the object and the tomographic images of the object are captured, the two-dimensional scans in the second image capturing mode requiring a shorter time than that required for the two-dimensional scans in the first image capturing mode, the capturing of the tomographic images in the first image capturing mode being performed after performing adjustment of an image capturing condition necessary for capturing the tomographic images in the first image capturing mode, the adjustment being based on the tomographic images captured in the second image capturing mode.

In the present application, examples of adjustment of the image capturing condition necessary for capturing tomographic images in the first image capturing mode include various adjustment operations that are performed before the capturing of tomographic images to obtain optimum tomographic pictures of an ocular fundus, such as alignment of the tomographic image capturing device and a subject's eye as the object, focus adjustment to move the position of a focusing lens for focusing in accordance with the diopter scale of a subject's eye, reference mirror positioning to move the position of a reference mirror to match the optical path lengths of the measurement optical system and reference optical system so that interference light is generated by superposition of the measurement light and reference light, and dispersion compensation glass determination to select an appropriate dispersion compensation glass for compensating for refractive index dispersion that causes blurred tomographic images.

According to the above invention (Invention 1), the second image capturing mode is provided to capture tomographic images by the two-dimensional scans which require a shorter time than that in the first image capturing mode and therefore the adjustment of the image capturing condition can be completed in a short time by performing, in the second image capturing mode, the adjustment of image capturing condition necessary for capturing tomographic images in the first image capturing mode. Moreover, an optimum image capturing condition can be determined because the capturing of tomographic images in the second image capturing mode is performed by the two-dimensional scans, rather than by the one-dimensional scan at the center position or the like of the raster scans as in the prior art, and tomographic pictures that almost entirely cover the image capturing site can thereby be observed during the adjustment of image capturing condition.

The scanning region in the second image capturing mode is preferably a region that includes a region of interest within the scanning region in the first image capturing mode. The “region of interest” as used herein refers to a region that represents a change in form of the image capturing object within the scanning region in the first image capturing mode.

According to a second aspect of the invention, when the tomographic images are captured in the first image capturing mode, the region of interest within a target region to be scanned is included in a target to be scanned in the second image capturing mode. Therefore, information sufficient to adjust the image capturing condition necessary when capturing the tomographic images in the first image capturing mode can be obtained from the tomographic images captured in the second image capturing mode. Here, the scanning region in the second image capturing mode may be wider than or narrower than the scanning region in the first image capturing mode, provided that the scanning region in the second image capturing mode includes the region of interest within the scanning region in the first image capturing mode.

According to a third aspect, the two-dimensional scans in the first image capturing mode are preferably raster scans. According to a fourth aspect, the two-dimensional scans in the second image capturing mode are preferably scans thinned from the raster scans in the first image capturing mode.

The scans may be scans that scan four sides of a rectangular region including the region of interest within the scanning region in the first image capturing mode (fifth aspect) or may also be scans that scan one or two diagonals of a rectangular region including the region of interest within the scanning region in the first image capturing mode (sixth aspect).

The tomographic image capturing device may further have a third image capturing mode in which the measurement light is one-dimensionally scanned to be incident to the object and a tomographic image of the object is captured, wherein a first adjustment operation may be performed on the basis of the tomographic image captured in the third image capturing mode and a second adjustment operation may then be performed on the basis of the tomographic images captured in the second image capturing mode (seventh aspect), or the tomographic image capturing device may include a display means that displays tomographic pictures of the object generated on the basis of the captured tomographic images, wherein the display means may be configured to be switchable between a first display mode and a second display mode in the second image capturing mode, wherein the first display mode may be a mode in which only one tomographic picture including a certain position of interest of the object is displayed from among the tomographic pictures generated on the basis of the tomographic images captured in the second image capturing mode and the second display mode may be a mode in which the tomographic pictures generated on the basis of the tomographic images captured in the second image capturing mode are in turn displayed, wherein a first adjustment operation may be performed on the basis of the tomographic picture displayed in the first display mode and a second adjustment operation may then be performed on the basis of the tomographic pictures displayed in the second display mode (eighth aspect).

In the present application, the first adjustment operation means performing dispersion compensation glass determination to select an appropriate dispersion compensation glass in order to compensate for refractive index dispersion that causes blurred tomographic images and performing focus adjustment to move the position of a focusing lens for focusing in accordance with the diopter scale of a subject's eye. In the present application, the second adjustment operation means performing focus adjustment to move the position of a focusing lens for focusing in accordance with the diopter scale of a subject's eye and performing reference mirror positioning to move the position of a reference mirror to match the optical path lengths of the measurement optical system and reference optical system so that interference light is generated by superposition of the measurement light and reference light.

The, first adjustment operation, in which the adjustment can be appropriately performed on the basis only of a specific tomographic picture, and the second adjustment operation, in which the adjustment can be more appropriately performed rather on the basis of a plurality of tomographic pictures obtained through the two-dimensional scans, can be separately performed, and a more appropriate image capturing condition can thereby be determined in a short time.

According to a ninth aspect, the tomographic image capturing device preferably includes a storage means that stores the tomographic images captured in the second image capturing mode. Conventionally, tomographic images acquired for adjustment of the image capturing condition have not been used for other purposes than the adjustment, but according to this aspect, data of the tomographic images captured in the second image capturing mode can be stored and the stored data can thus be used for correction of the positioning of the tomographic pictures generated from the tomographic images captured in the first image capturing mode and/or used as thumbnail pictures.

Advantageous Effect of the Invention

According to the tomographic image capturing device of the present invention, adjustment of the image capturing condition can be completed in a short time to determine an optimum image capturing condition.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an optics view illustrating the overall configuration of a tomographic image capturing device according to a first embodiment of the present invention.

FIG. 2 is an explanatory view illustrating a scanning pattern in a main image capturing mode of the embodiment.

FIG. 3 is an explanatory view illustrating a scanning pattern in a preliminary image capturing mode of the embodiment.

FIG. 4 is an explanatory view illustrating a flow of switching from the preliminary image capturing mode to the main image capturing mode in the embodiment.

FIG. 5 is an explanatory view illustrating a flow of switching from an adjustive image capturing mode to a preliminary image capturing mode and switching from the preliminary image capturing mode to a main image capturing mode in a second embodiment of the present invention.

FIG. 6 is a set of explanatory views illustrating modified examples of scanning patterns in the preliminary image capturing mode.

FIG. 7 is a set of explanatory views illustrating scanning patterns at the time of adjusting the image capturing condition and at the time of image capturing in a conventional tomographic image capturing device.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

<First Embodiment>

Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is an optics view illustrating the overall configuration of a tomographic image capturing device according to the first embodiment of the present invention. The tomographic image capturing device according to the present embodiment, which can be applied to an ocular fundus of a subject's eye E as the image capturing object, is to capture tomographic images of a desired region of the ocular fundus by raster scans. The part denoted by reference numeral 10 is a demultiplexing/multiplexing optical system. This optical system may be provided with a broadband low-coherence light source 11 that comprises, for example, a super-luminescent diode (SLD) and emits light of a temporal coherence length of about several micrometers to several tens of micrometers at a wavelength of 700 nm to 1,100 nm.

The low-coherence light generated from the low-coherence light source 11 passes through a light power adjustment mechanism 12, in which the light power is adjusted, and is incident to an optical coupler 13 via an optical fiber 13 a and then introduced into a beam splitter 20 as a splitting optical element via an optical fiber 13 b and collimator lens 14. Demultiplexing and/or multiplexing may also be performed using an optical circulator as substitute for the optical coupler 13.

The light incident to the beam splitter 20 is split into reference light and measurement light. The measurement light is incident to a focusing lens 31, which is to focus the measurement light on the ocular fundus of the subject's eye E. The measurement light to be focused on the ocular fundus is reflected by a mirror 32, passes through a lens 33, and is scanned in an arbitrary direction by an x-axis scanning mirror (galvanometer mirror) 34 and y-axis scanning mirror (galvanometer mirror) 35. The measurement light scanned by the x-axis and y-axis scanning mirrors 34 and 35 passes through a scanning lens 36, is reflected by a dichroic mirror 37, and then passes through an objective lens 38 to be incident to the ocular fundus, which is thus scanned by the measurement light in the x-direction and y-direction. The measurement light reflected by the ocular fundus tracks back the above path to return to the beam splitter 20.

In such an optical system, the focusing lens 31, mirror 32, lens 33, x-axis scanning mirror 34, y-axis scanning mirror 35, scanning lens 36, dichroic mirror 37 and objective lens 38, which are located downstream the beam splitter 20, may constitute a measurement optical system 30 of the tomographic image capturing device.

On the other hand, the reference light split by the beam splitter 20 is reflected by a mirror 41 and then passes through a dispersion compensation glass for objective lens 42 and lenses 43 and 44. Thereafter, the reference light is reflected by a mirror 45 and passes through a subject's eye dispersion compensation glass 50 that compensates for the refractive index dispersion of the subject's eye E as the object. Then, the reference light is reflected by a dichroic mirror 46, passes through a focusing lens 47 and variable aperture 48, and reaches a reference mirror 49. The variable aperture 48 may adjust the light power. To adjust the optical path length, the focusing lens 47, variable aperture 48 and reference mirror 49 can move in the optical axis direction in an integrated manner, as indicated by the horizontal arrow in FIG. 1. The reference light reflected by the reference mirror 49 tracks back the above optical path to return to the beam splitter 20.

In the present embodiment, the focusing lens 31, lens 33, scanning lens 36 and objective lens 38 of the measurement optical system 30 may correspond respectively to the lens 43, lens 44, focusing lens 47 and dispersion compensation glass for objective lens 42 of the reference optical system 40, and respective dispersion characteristics may be the same or equivalent. The mirror 32, x-axis scanning mirror 34, y-axis scanning mirror 35 and dichroic mirror 37 of the measurement optical system 30 may correspond respectively to the mirror 41, mirror 45, reference mirror 49 and dichroic mirror 46 of the reference optical system 40, and respective dispersion characteristics may also be the same or equivalent. The dispersion characteristics of the subject's eye E and the dispersion characteristics of the subject's eye dispersion compensation glass 50 may also be the same or equivalent.

In such an optical system, the mirror 41, dispersion compensation glass for objective lens 42, lenses 43 and 44, mirror 45, subject's eye dispersion compensation glass 50, dichroic mirror 46, focusing lens 47 and reference mirror 49 may constitute a reference optical system 40 of the tomographic image capturing device. The reference mirror 49 may act as a reference object.

The measurement light and reference light returned to the beam splitter 20 are superposed with each other to be interference light, which passes through the collimator lens 14 and optical coupler 13 and is incident to a spectroscope 16 via an optical fiber 13 c. The spectroscope 16 may have a diffraction grating 16 a, imaging lens 16 b, line sensor 16 c, and other necessary components. The interference light is diffracted by the diffraction grating 16 a into a spectrum in accordance with the wavelength of the low-coherence light and forms an image on the line sensor 16 c by the imaging lens 16 b.

Signals from the line sensor 16 c may be subjected to signal processing, including Fourier transformation, performed by a tomographic picture forming means that is realized using one or more CPUs of a computer 17 and the like. This signal processing generates a depth signal that represents information in the depth direction (z-direction) of the ocular fundus. When scanning the ocular fundus, the interference light at each sampling time point allows the depth signal (A-scan picture) at the sampling time point to be obtained. Therefore, completion of one scanning can form a two-dimensional tomographic picture (B-scan picture) that comprises a z-direction picture (A-scan picture) along the scanning direction. The formed tomographic picture (B-scan picture) can be displayed on the display 18. The formed tomographic picture can also be stored in a storage part (not illustrated) of the computer 17.

The tomographic image capturing device according to the present embodiment may perform some adjustments of the image capturing condition to optimize the image capturing condition when actually capturing tomographic images. Examples of adjustments of the image capturing condition include, for example, alignment of the tomographic image capturing device and the subject's eye E as the object, focus adjustment to move the position of the focusing lens 31 for focusing in accordance with the diopter scale of the subject's eye E, reference mirror positioning to move the position of the reference mirror 49 to match the optical path lengths of the measurement optical system and reference optical system so that interference light is generated by superposition of the measurement light and reference light, and dispersion compensation glass determination to select an appropriate dispersion compensation glass 50 for compensating for refractive index dispersion that causes blurred tomographic images.

The tomographic image capturing device according to the present embodiment may be configured to be switchable between a preliminary image capturing mode (second image capturing mode) and a main image capturing mode (first image capturing mode). In the preliminary image capturing mode, tomographic images for adjusting the image capturing condition are captured. In the main image capturing mode, tomographic images for actually obtaining tomographic pictures of a desired region (scanning region) of the ocular fundus are obtained after an optimum image capturing condition is determined by the adjustment of image capturing condition. Specifically, the tomographic image capturing device may capture tomographic images using different scanning patterns in the preliminary image capturing mode and in the main image capturing mode and can switch between the preliminary image capturing mode and the main image capturing mode by an image capturing mode switching operation.

In the main image capturing mode, as illustrated in FIG. 2, the scanning region as a whole may be raster-scanned. In the main image capturing mode of the present embodiment, the scans may be performed 256 times in total in the fast axis direction (x-direction), but are not limited thereto and may be appropriately modified in accordance with the image capturing object, purpose of image capturing, and/or size of the scanning region.

In the preliminary image capturing mode, as illustrated in FIG. 3, the scanning interval in the slow axis direction (y-direction) may be extended thereby to perform scans of a coarser scanning density than that in the main image capturing mode, that is, to perform scans thinned from the scans in the fast axis direction (x-direction) of the raster scans in the main image capturing mode. In the preliminary image capturing mode of the present embodiment, the scans may be performed 11 times in total in the fast axis direction (x-direction), but are not limited thereto and may be appropriately modified in accordance with the image capturing object, purpose of image capturing, and/or size of the scanning region. Optimization of the image capturing condition can be appropriately carried out when the number of scans is sufficient for perceiving a change in shape of the object at least within the scanning region. It is to be noted, however, that the number of scans in the preliminary image capturing mode may preferably be set within a range of ½ to 1/20 of the number of scans in the main image capturing mode because the preliminary image capturing mode is expected to have an effect of reducing the time required for capturing the tomographic images for adjustment of the image capturing condition by making the scanning density coarser than that in the main image capturing mode, that is, an effect of completing the adjustment of image capturing condition in a short time.

In the present embodiment, the scanning region in the preliminary image capturing mode may be a region that is the same as the scanning region in the main image capturing mode. Therefore, the region of interest within the scanning region in the main image capturing mode is included in the scanning region in the preliminary image capturing mode, as will be understood. Here, the region of interest refers to a region that represents a change in form of the image capturing object (ocular fundus of the subject's eye E) within the scanning region in the main image capturing mode.

In the present embodiment, when displaying the tomographic pictures of the ocular fundus of the subject's eye E which are generated from the tomographic images captured in the preliminary image capturing mode, two display modes of a selective display mode and a sequential display mode may be prepared. These display modes can be switched using a display mode switching button (not illustrated). The selective display mode refers to a display scheme in which the display 18 displays only one tomographic picture including a certain position of interest of the object from among the tomographic pictures generated on the basis of the tomographic images captured in the preliminary image capturing mode. In the present embodiment, only one tomographic picture generated on the basis of the tomographic image captured through a scan at the center position in the y-direction of the scanning region (scan of No. 6 in FIG. 3) maybe displayed in a repetitive manner. The sequential display mode refers to a display scheme in which the tomographic pictures generated on the basis of the tomographic images captured in the preliminary image capturing mode are in turn sequentially displayed on the display 18. In the present embodiment, 11 tomographic pictures generated on the basis of the tomographic images captured through all the scans (scans of No. 1 to No. 11 in FIG. 3) may be in turn displayed in a repetitive manner.

In the present embodiment, the adjustment of image capturing condition may be divided into two stages of a first adjustment operation and a second adjustment operation, and the previously-described selective display mode may be used to perform the first adjustment operation while the sequential display mode may be used to perform the second adjustment operation. The first adjustment operation may include performing dispersion compensation glass determination to select an appropriate dispersion compensation glass 50 in order to compensate for refractive index dispersion that causes blurred tomographic images and performing focus adjustment to move the position of the focusing lens 31 for focusing in accordance with the diopter scale of the subject's eye E. The second adjustment operation may include performing focus adjustment to move the position of the focusing lens 31 for focusing in accordance with the diopter scale of the subject's eye E and performing reference mirror positioning to move the position of the reference mirror 49 to match the optical path lengths of the measurement optical system and reference optical system so that interference light is generated by superposition of the measurement light and reference light. Thus, the first adjustment operation, in which the adjustment can be appropriately performed on the basis only of the one specific tomographic picture, and the second adjustment operation, in which the adjustment can be more appropriately performed rather on the basis of the plurality of tomographic pictures obtained through the two-dimensional scans, can be separately performed, and a more appropriate image capturing condition can thereby be determined in a short time.

Description will now be directed to a flow of the adjustment of image capturing condition using switching between the preliminary image capturing mode and the main image capturing mode and switching between the selective display mode and the sequential display mode in the present embodiment. As illustrated in FIG. 4(a), first, the first adjustment operation may be performed in the preliminary image capturing mode, but the first adjustment operation is capable of appropriate adjustment based only on the one specific tomographic picture. In this operation, therefore, the display 18 may be set in the selective display mode and repeatedly display only a tomographic picture T₆ that is generated on the basis of the tomographic image captured by the scan of No. 6.

After completion of the first adjustment operation in the selective display mode, the image capturing scheme may remain in the preliminary image capturing mode while the display mode switching button may be pressed to switch the display 18 to the sequential display mode to perform the second adjustment operation in which, as illustrated in FIG. 4(b), the adjustment can be more appropriately performed rather on the basis of the plurality of tomographic pictures obtained through the two-dimensional scans. In the sequential display mode, the tomographic images T₁ to T₁₁ may be in turn displayed in a repetitive manner.

After completion of the second adjustment operation in the sequential display mode, the display mode switching button may be pressed to switch from the preliminary image capturing mode to the main image capturing mode in which, as illustrated in FIG. 4(c), 256 raster scans in total may be performed in the fast axis direction (x-direction) within the entire scanning region to capture tomographic images of the ocular fundus of the subject's eye E under the optimized image capturing condition.

As will be understood, the selective display mode and the sequential display mode are merely different in the display scheme for the tomographic pictures. Regardless of whether the selective display mode or the sequential display mode is selected, the image capturing itself of tomographic images of the subject's eye E may be performed through 11 scans in total of No. 1 to No. 11 under the preliminary image capturing mode. In other words, even when the selective display mode is set, scans of No. 1 to No. 11 may be performed to capture the tomographic images necessary for generating the tomographic pictures T₁ to T₁₁, rather than performing only the scan of No. 6 to capture only the tomographic image for generating the tomographic picture T₆.

Data of the tomographic images captured in the preliminary image capturing mode and the tomographic pictures generated based thereon may be stored in a storage part (not illustrated) of the computer 17. The tomographic pictures acquired by image capturing in the preliminary image capturing mode are those obtained through raster scans at a speed of several times to several tens of times higher than that for the tomographic pictures obtained by image capturing in the main image capturing mode. Therefore, image capturing is possible while suppressing the position shift due to involuntary eye movements in the slow axis direction. Each tomographic picture acquired in the preliminary image capturing mode can be used as the basis to perform correction of the position shift for relocation of the tomographic pictures acquired in the first image capturing mode and it is thus possible to obtain high-density pictures from which the influence of involuntary eye movements is eliminated.

As described above, according to the tomographic image capturing device of the present embodiment, the preliminary image capturing mode is provided to capture tomographic images through the two-dimensional scans in which the scanning density is coarser than that in the main image capturing mode, and the time required for the two-dimensional scans in the preliminary image capturing mode can be shorter than that for the two-dimensional scans in the main image capturing mode. Therefore, the adjustment of image capturing condition can be completed in a short time by performing, in the preliminary image capturing mode, the adjustment of image capturing condition necessary for capturing tomographic images in the main image capturing mode. Moreover, an optimum image capturing condition can be determined because the capturing of tomographic images in the preliminary image capturing mode is performed through the two-dimensional scans, though with a coarse scanning density, rather than through one-dimensional scan at the center position or the like of raster scans as in the prior art, and tomographic pictures that almost entirely cover the image capturing site can thereby be observed during the adjustment of image capturing condition.

<Second Embodiment>

Next, a second embodiment of the present invention will be described in detail with reference to the drawings. The overall configuration of the tomographic image capturing device according to the second embodiment is identical to that of the tomographic image capturing device according to the first embodiment and the description of the optical systems and others will be omitted. The same or similar elements, components and devices as in the first embodiment are denoted by the same reference numerals and the same term is used as having the same meaning. Different aspects from those of the tomographic image capturing device according to the first embodiment will be described below.

In the tomographic image capturing device according to the present embodiment, the adjustment of image capturing condition is divided into a first adjustment operation and a second adjustment operation. The tomographic image capturing device is configured to be switchable among an adjustive image capturing mode in which a tomographic image for performing the first adjustment operation is captured, a preliminary image capturing mode in which tomographic images for performing the second adjustment operation are captured, and a main image capturing operation in which tomographic images for actually obtaining tomographic pictures of a scanning region are captured after an optimum image capturing condition is determined by the first and second adjustment operations. Specifically, the tomographic image capturing device can capture tomographic images using different scanning patterns in these modes and switch among the adjustive image capturing mode, the preliminary image capturing mode and the main image capturing mode by an image capturing mode switching operation.

The scanning patterns in the preliminary image capturing mode and in the main image capturing mode are the same as those of the first embodiment. The adjustive image capturing mode is an image capturing mode in which the measurement light is one-dimensionally scanned to be incident to an object and a tomographic image of a position of interest of the object is captured. For example, the center position in the y-direction of the scanning region is the position of interest, which is one-dimensionally scanned in the x-direction. As will be understood, the position of interest may be appropriately changed in accordance with the image capturing object, purpose of image capturing, and/or size of the scanning region.

It is not necessary to obtain a plurality of tomographic pictures by two-dimensionally scanning the scanning region because the first adjustment operation can be appropriately performed on the basis only of one specific tomographic picture. Moreover, the tomographic image can be captured in a shorter time by one-dimensionally scanning the position of interest within the scanning region than by two-dimensionally scanning the scanning region. Thus, the adjustive image capturing mode for one-dimensional scanning within the scanning region is provided separately from the preliminary image capturing mode. Therefore, the first adjustment operation, in which the adjustment can be appropriately performed on the basis only of the one specific tomographic picture, and the second adjustment operation, in which the adjustment can be more appropriately performed rather on the basis of the plurality of tomographic pictures obtained through the two-dimensional scans, can be separately performed in the adjustive image capturing mode and the preliminary image capturing mode, respectively, and a more appropriate image capturing condition can thereby be determined in a short time.

In the first embodiment, two modes of the selective display mode and the sequential display mode are prepared in the preliminary image capturing mode as the display schemes for tomographic pictures on the display 18 so that the first adjustment operation and the second adjustment operations can be separately performed. In the present embodiment, however, the display scheme capable of switching to the selective display mode is unnecessary because the adjustive image capturing mode is provided. Therefore, the following description will be made on the assumption that the display scheme in the preliminary image capturing mode is in the sequential display mode.

Description will be directed to a flow of the adjustment of image capturing condition using switching among the adjustive image capturing mode, the preliminary image capturing mode and the main image capturing mode. As illustrated in FIG. 5(a), first, the first adjustment operation may be performed in the adjustive image capturing mode. In the adjustive image capturing mode, the display 18 may repeatedly display a tomographic picture T_(c) that is generated on the basis of the tomographic image captured by a scan in the x-direction. This scan is performed at the center position C in the y-direction of the scanning region.

After completion of the first adjustment operation in the adjustive image capturing mode, the display mode switching button may then be pressed to switch from the adjustive image capturing mode to the preliminary image capturing mode in which, as illustrated in FIG. 5(b), the second adjustment operation is performed while confirming tomographic images T₁ to T₁₁ that are in turn displayed on the display 18 in a repetitive manner.

After completion of the second adjustment operation in the preliminary image capturing mode, the display mode switching button may be pressed again to switch from the preliminary image capturing mode to the main image capturing mode in which, as illustrated in FIG. 5(c), 256 raster scans in total may be performed in the fast axis direction (x-direction) within the entire scanning region to capture tomographic images of the ocular fundus of the subject's eye E under the optimized image capturing condition.

As described above, according to the tomographic image capturing device of the present embodiment, the first adjustment operation in which the adjustment can be appropriately performed on the basis only of the one specific tomographic picture may be performed in the adjustive image capturing mode, and the second adjustment operation in which the adjustment can be more appropriately performed rather on the basis of the plurality of tomographic pictures obtained through the two-dimensional scans may be performed in the preliminary image capturing mode. This allows a more appropriate image capturing condition to be determined in a short time.

The tomographic image capturing device according to the present invention has been described hereinbefore with reference to the drawings, but the present invention is not limited to the above embodiments and various modified embodiments are possible. For example, in one or more embodiments as described above, the tomographic image capturing device captures tomographic images of an ocular fundus by raster scans, but the present invention is not limited to this. Spiral scan and other scan schemes may also be employed.

In one or more embodiments as described above, scans in the preliminary image capturing mode are performed by being thinned from the scans in the fast axis direction (x-direction) of the raster scans in the main image capturing mode, but the present invention is not limited to this. It may suffice that the two-dimensional scans in the preliminary image capturing mode require a shorter time than that required for the two-dimensional scans in the main image capturing mode. For example, the time required for the two-dimensional scans in the preliminary image capturing mode may be shortened by narrowing the scanning region than that in the main image capturing mode while maintaining the same scanning density as in the main image capturing mode. The present invention also encompasses cases in which the time required for the two-dimensional scans in the preliminary image capturing mode can be shortened by coarsely setting the scanning density even with a wider scanning region in the preliminary image capturing mode than that in the main image capturing mode. Thus, when the scanning region in the preliminary image capturing mode is a different region from that in the main image capturing mode, the region of interest within the scanning region in the main image capturing mode may be set to be included in the scanning region in the preliminary image capturing mode, and information sufficient to adjust the image capturing condition necessary when capturing the tomographic images in the main image capturing mode can thereby be obtained from the tomographic images captured in the preliminary image capturing mode.

Furthermore, other scanning patterns may be employed in the preliminary image capturing mode, provided that the two-dimensional scans in the preliminary image capturing mode require a shorter time than that required for the two-dimensional scans in the main image capturing mode. For example, as illustrated in FIG. 6(a), the scanning pattern may be set to scan four sides of a rectangular region that includes the region of interest within the scanning region to be a target for raster scans in the main image capturing mode, or as illustrated in FIG. 6(b), the scanning pattern may be set to scan one or two diagonals of a rectangular region that includes the region of interest within the scanning region to be a target for raster scans in the main image capturing mode, or the scanning pattern may be obtained by combining them. The present invention also encompasses cases in which the scanning direction in the main image capturing mode and the scanning direction in the preliminary image capturing mode are orthogonal to each other. Even with such a scanning pattern, it is possible to capture one or more tomographic images that represent a change in shape of the object within the scanning region and such a pattern can be employed as the scanning pattern in the preliminary image capturing mode.

DESCRIPTION OF REFERENCE NUMERALS

-   E Subject's eye (object) -   10 Demultiplexing/multiplexing optical system -   11 Low-coherence light source -   12 Light power adjustment mechanism -   13 Optical coupler -   14 Collimator lens -   20 Beam splitter -   30 Measurement optical system -   31 Focusing lens -   34 X-axis scanning mirror -   35 Y-axis scanning mirror -   36 Scanning lens -   37 Dichroic mirror -   38 Objective lens -   40 Reference optical system -   42 Dispersion compensation glass for objective lens -   46 Dichroic mirror -   47 Focusing lens -   48 Variable aperture -   49 Reference mirror -   50 Subject's eye dispersion compensation glass 

The invention claimed is:
 1. A tomographic image capturing device configured to: split light from a light source into measurement light and reference light; cause the measurement light and the reference light to be incident to an object and a reference object, respectively; and capture tomographic images of the object on a basis of interference light generated by superposition of the measurement light reflected from the object and the reference light reflected from the reference object, the tomographic image capturing device having a first image capturing mode and a second image capturing mode, the first and second image capturing modes each being a mode in which the measurement light is two-dimensionally scanned to be incident to the object and the tomographic images of the object are captured, the two-dimensional scans in the second image capturing mode requiring a shorter time than that required for the two-dimensional scans in the first image capturing mode, and a scanning region in the second image capturing mode being a region that includes a region of interest within a scanning region in the first image capturing mode, and the capturing of the tomographic images in the first image capturing mode being performed after performing adjustment of an image capturing condition necessary for capturing the tomographic images in the first image capturing mode, the adjustment being based on the tomographic images captured in the second image capturing mode, wherein the region of interest is a region that represents a change in form of the object within the scanning region in the first image capturing mode.
 2. The tomographic image capturing device as recited in claim 1, wherein the two-dimensional scans in the first image capturing mode are raster scans.
 3. The tomographic image capturing device as recited in claim 2, wherein the two-dimensional scans in the second image capturing mode are scans thinned from the raster scans in the first image capturing mode.
 4. The tomographic image capturing device as recited in claim 3, wherein the tomographic image capturing device further has a third image capturing mode in which the measurement light is one-dimensionally scanned to be incident to the object and a tomographic image of the object is captured, wherein a first adjustment operation is performed on a basis of the tomographic image captured in the third image capturing mode and a second adjustment operation is then performed on a basis of the tomographic images captured in the second image capturing mode.
 5. The tomographic image capturing device as recited in claim 3, wherein the tomographic image capturing device includes a display means that displays tomographic pictures of the object generated on a basis of the captured tomographic images, wherein the display means is configured to be switchable between a first display mode and a second display mode in the second image capturing mode, wherein the first display mode is a mode in which only one tomographic picture including a certain position of interest of the object is displayed from among the tomographic pictures generated on the basis of the tomographic images captured in the second image capturing mode and the second display mode is a mode in which the tomographic pictures generated on the basis of the tomographic images captured in the second image capturing mode are in turn displayed, wherein a first adjustment operation is performed on a basis of the tomographic picture displayed in the first display mode and a second adjustment operation is then performed on a basis of the tomographic pictures displayed in the second display mode.
 6. The tomographic image capturing device as recited in claim 1, wherein the two-dimensional scans in the second image capturing mode are scans that scan four sides of a rectangular region including a region of interest within a scanning region in the first image capturing mode.
 7. The tomographic image capturing device as recited in claim 1, wherein the two-dimensional scans in the second image capturing mode are scans that scan one or two diagonals of a rectangular region including a region of interest within a scanning region in the first image capturing mode.
 8. The tomographic image capturing device as recited in claim 1, wherein the tomographic image capturing device includes a storage means that stores the tomographic images captured in the second image capturing mode. 